While there are numerous exercise activities that one may participate in, exercise may be broadly broken into the categories of aerobic exercise and anaerobic exercise. Aerobic exercise generally refers to activities that substantially increase the heart rate and respiration of the exerciser for an extended period of time. This type of exercise is generally directed to enhancing cardiovascular performance. Such exercise usually includes low or moderate resistance to the movement of the individual. For example, aerobic exercise includes activities such as walking, running, jogging, swimming or bicycling for extended distances and extended periods of time.
Anaerobic exercise generally refers to exercise that strengthens skeletal muscles and usually involves the flexing or contraction of targeted muscles through significant exertion during a relatively short period of time and/or through a relatively small number of repetitions. For example, anaerobic exercise includes activities such as weight training, push-ups, sit-ups, pull-ups, or a series of short sprints.
To build skeletal muscle, a muscle group is contracted against resistance. The contraction of some muscle groups produces a pushing motion, while the contraction of other muscle groups produces a pulling motion. One type of exercise device that provides resistance to user's muscle contraction is a dumbbell. A dumbbell often includes a handle and weights at either end of the handle. In some cases, the weights are permanently affixed to the handle. Other types of dumbbells are adjustable where the weights can be removed and/or added to allow the user to adjust the amount of weight on the dumbbell.
One type of dumbbell is disclosed in U.S. Pat. No. 7,172,536 issued to Wei Ming Liu. In this reference, an adjustable dumbbell includes a number of weights each having a slot to receive end portions of a bar, and a number of latch rods slidably engaged in the weights and each having an inner end engageable into the slots of the weights and engageable with the bar, to anchor and latch a selected number of the weights to the bar, and to allow the selected weights to be moved in concert with the bar. The weights each have a spring member to bias and force the inner end of the latch rod to engage with and to latch the weights to the bar. The weights each include a panel having an orifice to slidably receive the latch rod, and to anchor the latch rod to the panel when the catch of the knob is rotated relative to the panel. Other types of dumbbells are described in U.S. Pat. No. 6,500,101 issued to James Chen, U.S. Patent Publication No. 2004/0005968 issued to Douglas A. Crawford, et al., U.S. Patent Publication No. 2012/0115689 issued to William Dalebout, et al., and WIPO International Publication No. WO/1994/017862 issued to Carl K. Towley. Each of these documents are herein incorporated by reference in their entirety for all that they contain.